When carrying out testing or other operations in deep bores, such as gas and oil wells, test equipment or other apparatus such as, for example, a casing perforating gun assembly, may be mounted on an end portion of a string of tubular sections, known as tubulars. The apparatus is lowered into the bore on the end of the string, the length of the string being increased by the addition of further tubulars, which are threaded together to define a continuous internal bore between the apparatus and the surface. As the successful running of certain tests, and the operation of many forms of apparatus, relies on the integrity of the string it is essential that the string is fluid tight. However, as the string is being lowered into the bore it is desirable that the string is filled with the fluid or mud in the well bore, surrounding the string. Accordingly, it is necessary to provide a tool which will allow fluid to flow into the string but which tool may also be activated to close the string to allow the integrity of the string to be tested. Existing tools for this purpose, in the form of tubing test valves, are located towards the lower end of the string and include flapper valves in the string bore which are pushed open if the external or annulus fluid pressure is greater than the internal string pressure, but are closed in the absence of such a pressure differential by a valve spring. The pressure integrity of the string above the valve may thus be tested by pumping down on top of the valve and monitoring the pressure at the surface. Such flapper valves generally operate satisfactorily, but the valve and valve seating restricts the internal bore diameter. Also, when the valve is open on run in, the well fluid flows over the valve sealing surfaces, which may result in wear to the surfaces and a loss of seal integrity.
A somewhat different valve arrangement is utilised in the Schlumberger Multicycle Circulating Valve (MCCV) tool, which is a recloseable valve, operating from internal fluid, or tubing pressure. The tool has an inner mandrel with a set of ports that can align with either reversing or circulating ports, or can close the ports for completion testing. The mandrel defines an internal piston and pressure cycles are used to move the mandrel between the three positions, the cycles moving a pin on a ratchet.
A tool operating in a generally similar manner is the Baker Sand Control Multi-Reverse Circulating Valve. Both this and the Schlumberger MCCV tool are of relatively large dimensions and thus restrict the inside diameter of the string in which they are fitted. Also, the relatively large outer diameters of the tools prevent them from being utilised in applications which require location of such tools below a well bore packer..
It is among the objects of the present invention to provide a tool which obviates or mitigates these disadvantages.